The research proposed deals with a most fundamental interaction in biochemistry, as yet incompletely described, between a transfer RNA specific for a given amino acid and the enzyme responsible for catalyzing the esterification reaction between these two molecules. What oligonucleotide regions of the tRNA does the protein contact in the recognition process? Carbon-13 nuclear magnetic resonance techniques will be used in attempts to provide an answer to this question in the case of tRNAglu and glutamyl synthetase, tRNAIVal and valine synthetase from E. coli. Undermodified tRNAglu from E. coli GM23 will be in vitro 13C-labeled in the accepting terminus, T-loop and anticodon loop. tRNAIVal, isolated and purified from the E. coli uracil auxotroph SO-187, contains uracil and uracil derivatives each with 13C enrichment at C4 carbons. tRNA will be specifically 13C-enriched at locations thought to be important in the recognition step. Two E. coli methylase mutants will be used to provide methyl deficient tRNAglu so that 13C-enriched methyl groups can be introduced into ribothymidine in one tRNAglu population and into the side chain of 5-methyl aminomethyl-2-thiouridine in another. The accepting adenosine terminus in these tRNAs will be replaced with adenosine labeled at carbon-2 in the adenine ring. Chemical shift and relaxation rate data on the enriched nuclei at these known locations when the tRNAs are complexed with cognate synthetase should provide structural and dynamic information on the properties of the complex in solution.